Ignition switch positions question

[hamster]

In the old days (especially with dynamos) you needed a decent run to charge the battery. Even from flat dead my Saab 9000 could fully recharge the battery in around 20 minutes at 50-60 mph around 2500 rpm.

However, if your battery is registering 8V then you have lost one cell (or possibly even two) in it. Typically this happens after a couple of cold nights.

I doubt if the trickle charger will help with this, as it's not about the battery's charge, but its ability to sink lots of current when cold.

Years ago when I was a student I kept my Mini's battery indoors at night, and when warm it was able to start the car over in the morning. If it was cold it would struggle to turn it over.

 

[taffy]

it could be a combination of weather, battery and alternator (and the fact it's a diesel which doesn't help)

http://wiki.answers.com/Q/Does_the_alte ... _is_idling

 

[IDB1]

The old battery, which only died because the second battery killed it, and the brand new battery both showed 8V with ignition on but engine not running.

With engine running it shows 14V (well.. a gnats under..)..

If it were losing charge every cold night then I'd replace it for being well on its way out (in fact, next year I want to replace it and re-add the second battery.. )..

 

[taffy]

Is that an 8v average over both batteries ?

If so it sounds like one is very much kaputt. If both are showing 8 then they may both have had it.

 

[IDB1]

Nooooo..

There's only one on there now...

When it had 2 (and was all fine and dandy), we had 8V at idle and 14V running...
When #2 died, it sucked the living s**t out of #1 overnight... repeatedly (until I found out what was happening and removed #2, which made #1 ok for some time (until the really harsh weather hit, in fact) but, ultimately, it died)..

With the single battery on there, right from fitting it, it only showed 8V without engine running (bearing in mind I am only using a dash voltmeter as indication - they aren't renowned for reliability or accuracy) and 14V with it running.

 

[MikeD]

Batteries are always less efficient if cold. You need plenty of amps to turn the engine over (and it's harder to turn over in the cold due to thicker oil), and if it's cold they can deliver less current. Two batteries in parallel can deliver more current, which is probably why it had them in the first place. It might just be that one battery simply isn't up to the job.

 

[IDB1]

Apparently there's a 'splitter' so that #2 runs things like towing electrics etc.. and charges secondary to the primary battery..
But it does have a connection to #1 since it'll suck it dry if it's knack'd..

It's run on 1 for 2 years with no probs (that I don't know the cause of - the first was #2 being fubar and the second was some burnt out wiring to the alternator.. all sorted now), I don't think that's an issue..
Not all Troopers had 2 batteries from the factory

 

[MikeD]

Is the single battery the same as one of the original two? Might be a bit marginal on capacity if so, especially after a couple of years (and actually going flat a few times - they don't like that). I'd have thought (not based on any Actual Knowledge, I should add) that one that was a little higher capacity than half the original pair (er, if that makes sense) would be the way forward. I'd be surprised if ones that came with a single battery actually had half the capacity. Although I'm used to surprise

Have you got a proper multimeter you can measure the voltage with?

 

[IDB1]

No multimeter.. both batteries (if fitted) are exactly the same and are of the correct size to turn a 3.1 4cyl diesel engine.. they big mofo's.

This battery hasn't gone properly flat, the last time it failed to start the truck was easily a year ago.. probably Summer '09 (when the alternator wiring shorted and burnt)..

We don't have an ongoing problem with a weak battery, it was just the other morning (after a month of short evening trips and a very cold night) it was sluggish to start and I'm pre-empting issues

 

[hamster]

Typically alternators give around 13.8V to charge. It sounds as though your voltmeter isn't far off the mark. 8V while the starter motor is turning over, I'd believe. But 8V when the ignition is on position 1 would not seem right. After your story of a burnt-out loom I think that something else is amiss. Using an ammeter to check how much is coming out of the battery on position 1 (or indeed when the ignition is off) might be a sensible check. I just have that nagging feeling that something else is staying on and dragging power.